View Single Post
Old 03-03-2014, 08:39 AM
CO Hunter's Avatar
CO Hunter CO Hunter is offline
Join Date: May 2010
Location: Colorado Springs
Posts: 130

How in the world do you get this stuff so fast, wow??? Are you an EE?

I haven't had chance to open it up yet. I emailed the guy from the yahoo group back and got this. By the way it seems like you two are on the same page.

"Look on page 55 Service Manual bottom Right Hand corner. If you follow circuit trace from Q3024 (2SC3102) collector lead towards the right, notice the trace leads to input of LPF----VU TX RF trace. Follow to R3069 33ohm 1 watt resistor which leads off to right from VU TX RF trace. Throght L3031
to D3019 and D3022 which lead off right to end of Schematic These are the two PIN diodes I mentioned , D3019 is the one I found bad in the rig I worked on. It is SMD components and not for the faint hearted soldering tech.
Should be 5vdc on tX at anode and about 0.2 to 0.5vdc drop at cathode or just do the usual check from circuit trace solder pad to anode, circuit trace solder pad to cathode, then anode to cathode, and the reverse ie; cathode to anode for ohmic checks. NOTE*****SMD capacitors at each end woould block DC continuity, but couples RF through, therefore in circuit checks okay.
Most DVMs have a diode check function selection or just measure the resistance thru. Should be close to infinite reverse biased. Will be low ohms resistance forward.

Also note from my previous email to you. The section that I'm pointing out is the UHF transmit path. If, the diodes not bad-----something in that section indicated most likely your problem as that is confined to 440Mhz. There is a separate section above it for two meters or VHF. At the end of that chain trace is the sensor for your SWR/FWD metering-----any variance in SWR readings would have to be outboard of that sensor-----hint hint.

One more note of interest. I had a similar problem on this radio when I was trying to TX on 70cm using a 2m home brew copper J-pole. The radio wold occasionally work on 70cm as I originally described the problem. However, at times when it would not TX on 70cm it would not TX on 2m. I did not use the radio in this manner too often for fear of damaging something. When I switched to an Arrow dual band j-pole the TX was flawless but I have not used it more than one time so far. Seems I am in the phase of more building/configuring things than talking these days.

I am not sure where this leaves me other than Yaesu tech facility as I do not posses the SMD tools nor skills. I very much appreciate the time you have taken with this.

In reply to my j-pole update here is what he said: "sometimes it's as simple as a resonant length of coax at 144 or 440 Mhz. and RF getting back into the transmitter on the 857. Bad ground, especially with a vertical antenna can be instigator. If, you have an external meter or a antenna analyzer, by process of elimination one could discover if it's RF getting back into circuits or if a component is bad. Even water getting in the coax from a leak at the PL 259 connectors outdoors can cause crazy intermittent.

I wish you the best of luck with your situation. Here I use a two step process: What is working-what is not working. What "can" cause it to exhibit these symptoms.

A leaky coax at the j-pole could have been at least part of the cause for that issue as that antenna had been up for a few years even though I did water proof it pretty well.

Unfortunately I am not near as versed in these type of diagnosis as you two are and then there is the matter of the SMD skills to fix it!!
1996 LX 450 OME heavy front/med rears, factory e-lockers, 285/75-16 Discoverer STT, home made t-case skid plate, ARB front bumper, XD9000i, Redline sliders, HID off road lights, Kenwood TM-D710

"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -- Benjamin Franklin
Reply With Quote